The invention concerns a process for the region-wise transfer of the decorative layer of a transfer foil, which decorative layer includes an adhesive layer which is activatable by radiation energy, from a carrier film for the decorative layer onto a substrate using a possibly heated stamping tool, wherein the adhesive layer is at least partially activated before the transfer foil passes into the stamping tool.
The invention further concerns a transfer foil which in particular is suitable for use in the transfer process according to the invention, which on a carrier film has a decorative layer which comprises a plurality of layer portions and which can be transferred region-wise onto a substrate under the action of pressure and possibly heat and whose surface that is remote from the carrier film is formed by an adhesive layer which is activatable by radiation energy.
When transferring the decorative layer of a transfer foil onto a substrate, it is necessary for the adhesive to be sufficiently activated in order to attain adequate adhesion of the decorative layer on the substrate. In that respect, the time required for activation of the adhesive layer quite crucially determines the speed of passage through the corresponding application machines.
In order to increase the machine speed, it is already known from WO 96/37368 for the heat-activatable adhesive layer of the decorative layer of a stamping or embossing foil to be preheated prior to the actual stamping or embossing operation in order in that way to at least partially activate the adhesive layer. In the known processxe2x80x94as usualxe2x80x94transfer of the decorative layer onto the substrate is effected in the regions in which the stamping tool acts on the stamping foil, while WO 96/37368 provides that the stamping tool is also heated. That procedure admittedly allows higher machine speeds to be attained. There is however the risk that, for example when the adhesive is excessively preheated, neat and clean region-wise application of the decorative layer to the substrate gives rise to difficulties because the decorative layer adheres to the substrate not only in the regions in which the stamping tool acts on the decorative layer but possibly also outside those regions, if the adhesive already has a sufficiently strong adhesion effect. That problem can occur in particular when using comparatively thick decorative layers, or decorative layers which are of a comparatively high level of mechanical stability and which for example have a metallisation thereon.
EP 0 741 370 B1 discloses a process for applying a security element to a substrate, in which the adhesive layer is brought into contact with the substrate and locally heated by the application of energy through the laminate structure, that is to say through the decorative layer, thereby seeking to provide that the decorative layer adheres to the substrate only at the heated locations, without any structures of the decorative layer being destroyed. In accordance with EP 0 741 370 B1, either laser radiation or light sources are used for the supply of energy. A laser beam can be guided in accordance with the desired pattern. When using light sources, the procedure involved has recourse either to masks or to exposure with addressable arrays consisting of laser or light emitting diodes. That known process certainly has the advantage that a very neat and clean and nonetheless only region-wise transfer of the decorative layer of a transfer foil from the carrier film of the transfer foil onto a substrate is possible, while the use of pressure in implementing transfer onto the substrate is substantially eliminated, to provide for careful treatment of the structures which are possibly present in the decorative layer. A disadvantage of that known procedure however is that comparatively low operating speeds must be reckoned to apply. When using masks or diode arrays, it even necessary under some circumstances to move the transfer foil and the substrate with a stepwise movement so that the mask or the array is stationary relative to the transfer foil, during the time required for activation of the adhesive layer.
Now, the object of the invention is to propose a process and a transfer foil which is suitable in particular for carrying out that process, with which there is on the one hand the possibility of increasing the machine speed by pre-activation of the adhesive layer, but at the same time also ensuring that neat and clean transfer of the decorative layer of the transfer foil also occurs only in the regions which are actually to be transferred.
In accordance with the invention, to attain that object, it is proposed that the process of the general kind set forth is so developed that before the transfer foil passes into the stamping tool the adhesive layer is activated by means of radiation energy only in the surface regions in which the decorative layer is to be transferred onto the substrate by means of the stamping tool.
In contrast to the teaching of WO 96/37368 in which pre-heating of the adhesive layer of the transfer foil is effected over substantially the entire surface area before it passes into the stamping tool, the present invention proposes that pre-heatingxe2x80x94similarly to the basic proposal of EP 0 741 370 B1xe2x80x94is effected only in a region-wise manner, in which respect however it is important that in actual fact preheating takes place before passing into the stamping tool. The process according to the invention therefore involves operating not only with activation of the adhesive but at the same time also by means of a suitable stamping tool, that is to say using suitable pressure.
By virtue of the additional application of pressure, it can very frequently be provided that a comparatively low level of radiation energy is already sufficient to pre-activate the adhesive to such an extent that the machine speed can be substantially increased. At the same time, region-wise pre-activation of the adhesive layer ensures that neat and clean region-wise stamping occurs, because the working conditions can be easily selected in such a fashion that the decorative foil adheres by way of the adhesive layer to the substrate only where the adhesive layer was actually also preheated.
It is particularly advantageous if the process according to the invention involves using a transfer foil whose decorative layer has an absorption layer only in the surface regions to be transferred onto the substrate, which absorption layer absorbs the radiation energy for effecting activation of the adhesive layer.
The transfer foil is therefor advantageously such that, in the surface regions to be transferred, it includes an additional layer portion, namely the absorption layer. Pre-activation of the adhesive layer then occurs only in the region of that absorption layer which suitably absorbs the radiation energyxe2x80x94and which naturally must be transferred to the adhesive layerxe2x80x94, wherein it is possible in that way, without involving particular apparatus complication and expenditure, to provide that the adhesive layer is pre-activated in actual fact only in the regions that are wanted. In particular, it is possible in accordance with the invention to eliminate the use of especially guided laser beams, as well as masks or diode arrays which are provided in accordance with EP 0 741 370 B1.
The effect of region-wise activation can be further improved in particular in the case of a transfer foil whose decorative layer is provided region-wise with an absorption layer, if the radiation energy for activating the adhesive layer acts on the decorative layer only in the surface regions which are intended for transfer onto the substrate, wherein the radiation energy for activating the adhesive layer advantageously acts by way of a mask or the like only on the surface regions of the decorative layer and adhesive layer, which are to be transferred onto the substrate.
In principle, it is possible to envisage using all possible kinds of activation of the adhesive layer. However, a procedure which is thought to be particularly desirable and thus of particular significance in a practical context is a procedure which involves using an adhesive layer which is activatable by means of thermal radiation, that is to say a so-called hot melt adhesive which softens and becomes sticky under the effect of heat.
Particularly when using a heat-activatable adhesive layer, it may be desirable to use laser radiation for activation purposes, in which case the laser radiation can possibly be deflected in accordance with the surface regions to be transferred. The use of laser radiation affords the advantage that it is possible to achieve very short heating times if the laser energy which acts is sufficiently high.
Finally, in accordance with the process of the invention, it is provided that the adhesive layer of the decorative layer is only pre-activated before the transfer layer passes into the stamping tool and a heated stamping tool serves for complete activation of the adhesive layer. That procedure permits comparatively high machine speeds. In that respect, the stamping tool may act over a large surface area or the entire surface area, or it may also act only in the regions in which the layer portions forming the decorative layer are to be transferred onto the substrate.
The invention further concerns a transfer foil, preferably a hot stamping foil, which is suitable in particular but not exclusively for the above-discussed process. This transfer foil which on a carrier or backing film has a decorative layer which comprises a plurality of layer portions and which can be transferred in a region-wise manner onto a substrate under the action of pressure and possibly heat and whose surface that is remote from the carrier film is formed by an adhesive layer which is activatable by radiation energy is distinguished in accordance with the invention in that the decorative layer has an absorption layer only in predetermined surface regions which are intended for transfer onto the substrate, which absorption layer absorbs the radiation energy causing activation of the adhesive layer.
The particularity of the transfer foil according to the invention is therefore that present in the decorative layer in a region-wise manner is an absorption layer which serves to absorb radiation energy serving for activation of the adhesive layer and in that way to provide for activation of the adhesive layer.
When a transfer foil of that kind is used in the process discussed in the opening part of this specification, it is particularly easy to achieve a clean and neat definition of the regions of the decorative layer, which are to be transferred. The transfer foil according to the invention however can also be usedxe2x80x94independently of the discussed processxe2x80x94by for example the adhesive layer being activated exclusively by way of the absorption layer. In a transfer foil of that kind, comparatively finely structured regions can be provided with the absorption layer. Even when the procedure involves irradiation over a large surface area and the use of stamping tools of large surface area, that nonetheless provides that in actual fact only the regions of the decorative layer, which are associated with the absorption layer, are transferred onto the substrate. When using a transfer foil in accordance with the invention therefore the effect that EP 0 741 370 B1 seeks to attain can be achieved with very simple means, while in particular there is no need in each case for the stamping apparatus used for transferring the decorative layer onto the substrate to be adapted to the specific configuration of the regions of the decorative layer, which are to be transferred.
In order to provide for a particularly good action of the radiation energy absorbed in the absorption layer, on the adhesive layer, it is desirable if the absorption layer is provided immediately adjoining the adhesive layer of the decorative layer.
It will be appreciated that the pigments or other additives which the absorption layer must contain in order to be able to suitably absorb the radiation energy do not always comply with the requirements in regard to the graphic or optical configuration of the decorative layer. If operation is implemented with thermal radiation, for example IR-radiation, the absorption layer contains generally dark, optically unattractive pigments or the like. Here it is desirable if, in accordance with the invention, the decorative layer, on the side of the absorption layer which faces towards the carrier film, has an opaque decorative layer portion which covers over the absorption layer after transfer of the decorative layer onto a substrate and which is desirably a reflection layer preferably having a structure with an optical diffraction effect, in particular a metal layer. Particularly when the arrangement has a reflection layer having a structure with an optical-diffraction effect, highly attractive graphical configurational arrangements can be embodied.
When the arrangement includes a reflection layer for covering over the absorption layer, which in use in fact forms the exposed surface of the decorative layer, it is desirable if the surface of the decorative layer, which faces towards the carrier film, is formed by a transparent protective lacquer layer, that is to say in other words the reflection layer is covered over by such a protective lacquer layer. A protective lacquer layer of that kind improves mechanical resistance and affords protection in particular for any structures having an optical-diffraction effect, which may be present, that is to say very fine structures.
In the multiplicity of situations of use of a transfer foil according to the invention it will be desirable if the absorption layer absorbs thermal radiation while the adhesive layer is formed by a heat-activatable material which is transmissive for the thermal radiation absorbed by the absorption layer. That configuration is desirable in particular when a reflection layer is present on the side of the decorative layer which is visible in use, the reflection layer preventing penetration of the radiation serving for activation purposes.
If in such a case the adhesive layer is transmissive for the thermal radiation absorbed by the absorption layer, irradiation of the transfer foil can be effected from the adhesive side. That also has the advantage that the radiation is then not unnecessarily weakened by the carrier film. The structure having a transparent adhesive layer and an absorption layer which is separate therefrom also affords the technical advantage that the adhesion effect of the adhesive layer is not adversely affected by the additives which are possibly present in the absorption layer.
In terms of practical implementation, it seems desirable if the absorption layer is formed by a lacquer layer containing the pigments which absorb the radiation energy serving for activation of the adhesive layer. The pigments that can be considered are for example carbon black, black or dark pigments etc. When using a heat-activatable adhesive layer, operation is more appropriately effected with infrared radiation for activation purposes, in which case then the arrangement is preferably such that the absorption layer absorbs infrared radiation of a wavelength for which the adhesive layer transmissive.